In an internal combustion engine of a motor vehicle, the crankshaft is coupled by a chain drive, a toothed belt drive or a gear drive to a drive sprocket which drives the camshaft essentially in synchronism with the crankshaft. By means of the camshaft, the valve opening times of the internal combustion engine are controlled. By means of an adjusting device of the type stated, the phase angle of the camshaft relative to the drive sprocket (and thus relative to the crankshaft) can be selectively modified in order to influence the combustion processes taking place in the internal combustion engine.
For this purpose, an actuating gear can act between the drive sprocket and the camshaft, it being possible to drive said actuating gear by means of an electric motor in order to adjust the camshaft relative to the drive sprocket. The use of an electric motor allows particularly accurate control.
In an arrangement of this kind, the actuating gear forms a summing gear, in which the drive sprocket is associated with a first input, an output element of the electric motor (e.g., a motor pinion) is associated with a second input, and the camshaft or a camshaft section (e.g., a camshaft flange) is associated with an output of the summing gear. It is advantageous here if the drive sprocket, the output element of the electric motor and the camshaft can be rotated coaxially with respect to one another to enable the entire unit consisting of the drive sprocket, the electric motor, the actuating gear and the camshaft to rotate about a common axis, referred to as the central axis.
In order to be able to adjust the camshaft relative to the drive sprocket, relatively high torques must be produced. To enable this function to be performed by a high speed electric motor of small size, the actuating gear must bring about a large reduction in the speed of the electric motor (based on a fixed drive sprocket). For this purpose, the actuating gear can have an internally toothed gearwheel and an externally toothed gearwheel in engagement with the latter, wherein the internally toothed gearwheel can be rotated about the central axis mentioned, and the externally toothed gearwheel is arranged eccentrically with respect to the central axis and, in this eccentric arrangement, can be driven so as to perform a circular motion about the central axis. Since the externally toothed gearwheel rolls on the internally toothed gearwheel, a relatively slow rotation of the externally toothed gearwheel (relative to the internally toothed gearwheel) is superimposed on the circular motion mentioned. If, in an arrangement of this kind, the externally toothed gearwheel has only slightly fewer teeth than the internally toothed gearwheel meshing therewith (e.g., a difference of 1 to 5 teeth), large ratios can thereby advantageously be formed (e.g., 60 to 300).
One problem of an actuating gear of this kind, however, is that the externally toothed gearwheel meshing with the internally toothed gearwheel is arranged eccentrically with respect to the central axis of the adjusting device. It is, therefore, not readily possible to transmit the circular motion of the externally toothed gearwheel to an input element or output element of the actuating gear (e.g., to the camshaft), which—as explained above—should each be arranged coaxially with the central axis.